Apparatus and method for virtual antenna mapping in multi-antenna system

ABSTRACT

An apparatus and a method for mapping virtual antennas and physical antennas in a wireless communication system. The method for mapping the virtual antennas and the physical antennas includes generating at least two virtual antenna signals for at least two virtual antennas. The method also includes generating at least two physical antenna signals by applying a corresponding matrix, which maps the at least two virtual antennas and the at least two physical antennas in many-to-many relation, to the at least two virtual antenna signals. The method further includes transmitting the at least two physical antenna signals over respective physical antennas.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application is related to end claims priority under 35U.S.C. §119(a) to a Korean patent application filed in the KoreanIntellectual Property Office on Mar. 15, 2010, and assigned Serial No.10-2010-0022768, the entire disclosure of which is hereby incorporatedby reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to an apparatus and a method forvirtual antenna mapping in a multi-antenna system. More particularly,the present invention relates to a virtual antenna mapping apparatus andmethod for uniform power distribution of a physical antenna in themulti-antenna system.

BACKGROUND OF THE INVENTION

Antennas of a wireless communication system are often classified aseither a virtual antenna called an antenna port, or a physical antennafor actually sending and receiving signals. In general, the virtualantenna and the physical antenna of the wireless communication systemcorrespond to each other by 1:1.

To detect a signal, a receiving stage estimates a channel between thevirtual antenna of a transmitting stage and the antenna of the receivingstage, and detects a size of the transmit signal and phase modulationusing the channel. The transmitting stage sends a reference signal pervirtual antenna so that the receiving stage can estimate the channel ofthe virtual antenna.

The reference signal is allocated for the receiving stage to estimatethe channel to the transmitting stage. To reject interference from atraffic channel, a resource is allocated separately from the trafficchannel. For example, when the transmitting stage includes four virtualantennas, it allocates the reference signal to each virtual antenna asshown in FIG. 1.

FIG. 1 depicts the resources of the reference signal in a conventionalmulti-antenna system. Hereafter, it is assumed that the multi-antennasystem employs an Orthogonal Frequency Division Multiplexing (OFDM)scheme.

When the transmitting stage includes four virtual antennas as shown inFIG. 1, it sends the reference signal over 0-th, fourth, seventh andeleventh OFDM symbols of the 0-th virtual antenna and the first virtualantenna. The transmitting stage sends the references signal over thefirst and eighth OFDM symbols of the second virtual antenna and thethird virtual antenna. That is, the transmitting stage allocates theresources of the reference signal to send the reference signal over thesame OFDM symbols of the 0-th virtual antenna and the first virtualantenna and to send the reference signal over the same OFDM symbols ofthe second virtual antenna and the third virtual antenna.

As sending the reference signal, the transmitting stage does nottransmit any signal at the same location as the reference signaltransmission location of the different virtual antennas in the resourcesof the virtual antennas.

As sending the reference signal per virtual antenna, the transmittingstage sends the reference signal with a transmit power four times thetransmit power of the traffic per resource block. In the tone carryingthe traffic, except for the reference signal, every virtual antenna ofthe transmitting stage sends the signal with the same transmit power.

Accordingly, the power used by the symbol carrying the reference signalper virtual antenna varies per virtual antenna. For example, when thetransmit power of the traffic is set to A, over the 0-th, fourth,seventh, and eleventh OFDM symbols in FIG. 1, the 0-th virtual antennaand the first virtual antenna consume the power of 4 A and the secondvirtual antenna and the third virtual antenna consume the power of 2 A.

Further, when the virtual antennas and the physical antennas correspondto each other by 1:1, the power imbalance of the virtual antennas causesimbalance in the power of the physical antennas. As a result, eachphysical antenna needs to be designed on different bases.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary aspect of the present invention to provide an apparatus and amethod for uniformly distributing power to physical antennas in amulti-antenna system.

Another aspect of the present invention is to provide an apparatus and amethod for mapping virtual antennas and physical antennas in amany-to-many correspondence in a multi-antenna system.

Another aspect of the present invention is to provide an apparatus and amethod for generating a corresponding matrix to map virtual antennas andphysical antennas in a many-to-many correspondence in a multi-antennasystem.

An aspect of the present invention is to provide an apparatus and amethod for generating a corresponding matrix to map virtual antennas andphysical antennas in a many-to-many correspondence by considering aprecoding vector in a multi-antenna system.

According to one aspect of the present invention, a method fortransmitting a signal at a transmitting stage of a wirelesscommunication system is provided. The method includes generating atleast two virtual antenna signals for at least two virtual antennas. Themethod also includes generating at least two physical antenna signals byapplying a corresponding matrix to the at least two virtual antennasignals, the corresponding matrix mapping the at least two virtualantennas and the at least two physical antennas in a many-to-manyrelation. The method further includes transmitting the at least twophysical antenna signals over respective physical antennas.

According to another aspect of the present invention, an apparatusmethod for transmitting a signal at a transmitting stage of a wirelesscommunication system is provided. The apparatus includes at least twophysical antennas. The apparatus also includes a signal generatorconfigured to generate at least two virtual antenna signals for at leasttwo virtual antennas. The apparatus further includes a virtual antennamapper configured to generate at least two physical antenna signals byapplying a corresponding matrix, which maps the at least two virtualantennas and the at least two physical antennas in a many-to-manyrelation, to the at least two virtual antenna signals. The virtualantenna mapper is also configured to provide the at least two physicalantenna signals to the respective physical antennas.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates resources of a reference signal in a conventionalmulti-antenna system;

FIG. 2 illustrates a method for sending a signal at a transmitting stagein a multi-antenna system according to an embodiment of the presentinvention; and

FIG. 3 illustrates the transmitting stage in the multi-antenna systemaccording to an embodiment of the present invention.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components and structures.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 3, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged wireless communication system.Embodiments of the present invention will be described herein below withreference to the accompanying drawings. In the following description,well-known functions or constructions are not described in detail sincethey would obscure the invention in unnecessary detail. Terms describedbelow, which are defined considering functions in the present invention,can be different depending on user and operator's intention or practice.Therefore, the terms should be defined on the basis of the disclosurethroughout this specification.

Exemplary embodiments of the present invention provide a technique foruniformly distributing power for at least two physical antennas in amulti-antenna system.

Hereinafter, the multi-antenna system is assumed to adopt OrthogonalFrequency Division Multiplexing (OFDM)/Orthogonal Frequency DivisionMultiple Access (OFDMA). Note that other communication schemes areequally applicable to the multi-antenna system.

It is assumed that the multi-antenna system employs a closed-loopspatial multiplexing scheme among multi-antenna transmission schemes.Notably, the present invention is equally applicable to variousmulti-antenna transmission schemes.

A transmitting stage of the multi-antenna system is assumed to includeN_(T) physical antennas and N_(K) virtual antennas. Herein, N_(T) andN_(K) can be of the same value or different values. Hereafter, it isassumed that N_(T) and N_(K) are four (4). That is, it is assumed thatthe transmitting stage includes four physical antennas and four virtualantennas.

To uniformly distribute power for the virtual antennas to the physicalantennas, the transmitting stage uses a corresponding matrix having thesame unitary properties with an absolute value one-half (½) of eachelement. For instance, the transmitting stage can map the virtualantennas and the physical antennas in many-to-many correspondence usingthe corresponding matrix based on Equation 1. Herein, the correspondingmatrix indicates a mathematical expression of the correspondence of thevirtual antennas and the physical antennas.

$\begin{matrix}{{{D\; F\; T\mspace{14mu} {Matrix}{\text{:}\mspace{14mu}\begin{bmatrix}z_{0} \\z_{1} \\z_{2} \\z_{3}\end{bmatrix}}} = {{\frac{1}{2}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- j} & {- 1} & j \\1 & {- 1} & 1 & {- 1} \\1 & j & {- 1} & {- j}\end{bmatrix}} \cdot \begin{bmatrix}y_{0} \\y_{1} \\y_{2} \\y_{3}\end{bmatrix}}}{{{Hadamard}\mspace{14mu} {Matrix}{\text{:}\mspace{14mu}\begin{bmatrix}z_{0} \\z_{1} \\z_{2} \\z_{3}\end{bmatrix}}} = {{\frac{1}{2}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & 1 & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}} \cdot \begin{bmatrix}y_{0} \\y_{1} \\y_{2} \\y_{3}\end{bmatrix}}}} & \left\lbrack {{Eqn}.\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, z_(i) (i=0, 1, 2, 3) denotes a signal of the physicalantenna, y_(i) (i=0, 1, 2, 3) denotes a signal of the virtual antenna,and i denotes an index of the physical antenna and the virtual antenna.

Using the corresponding matrix as stated above, the transmitting stagecan address a power imbalance of symbols carrying a reference signal bymapping the virtual antennas and the physical antennas by 4:4. That is,the transmitting stage can uniformly map the signals for the virtualantennas to the four physical antennas using the corresponding matrixand thus address the power imbalance of the physical antennas in thesymbols carrying the reference signal.

When the multi-antenna system rejects interference of a neighbor celland uses a precoding scheme to raise the transmission efficiency, thetransmitting stage sends the signal using a precoding matrix and thecorresponding matrix together based on Equation 2. Herein, Equation 2utilizes the DFT matrix of Equation 1 as the corresponding matrix. It isassumed that Equation 2 adopts the precoding matrix of the 0-th index ofthe rank 1 among 4 Tx CL-SM precode defined by 3GPP TS 36.211 of LTEstandard document.

$\begin{matrix}{\begin{bmatrix}z_{0} \\z_{1} \\z_{2} \\z_{3}\end{bmatrix} = {{\frac{1}{2}\begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- j} & {- 1} & j \\1 & {- 1} & 1 & {- 1} \\1 & j & {- 1} & {- j}\end{bmatrix}} \cdot {\frac{1}{2}\begin{bmatrix}1 \\1 \\1 \\1\end{bmatrix}} \cdot \left\lbrack W_{0} \right\rbrack}} & \left\lbrack {{Eqn}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Equation 2, z_(i) (i=0, 1, 2, 3) denotes the signal of the physicalantenna, i denotes the index of the physical antenna,

$\quad\begin{bmatrix}1 \\1 \\1 \\1\end{bmatrix}$

denotes the precoding matrix, and [w₀] denotes a signal before theprecoding.

When the precoding matrix and the corresponding matrix are used togetheras expressed in Equation 2, the signals of the virtual antennas fade andthe signal is not delivered to the antennas other than the 0-th physicalantenna. That is, the power imbalance occurs between the 0-th physicalantenna and the other antennas.

Hence, the transmitting stage designs the corresponding matrix tosatisfy the following conditions.

(1) The power of the physical antennas should be uniformly distributedfor the un-precoded reference signal.

(2) When the precoding matrix and the corresponding matrix are appliedconcurrently, precoding vectors of a precoding codebook should includeprecoding vectors of the power uniformly distributed of the physicalantennas, more than a reference number.

(3) The precoding vector satisfying the condition (2) should have anequivalent vector in the precoding codebook applied with thecorresponding matrix. Herein, the equivalent vector indicates the vectorof the constant phase difference between the elements in the precodingvector, for the sake of the same beamforming effect.

To meet the condition (1) and the condition (2) at the same time, themulti-antenna system designs the corresponding matrix to map two virtualantenna combinations to two physical antenna combinations. For instance,when the combination of the 0-th and second virtual antennas and thecombination of the first and third virtual antennas are used, thetransmitting stage can express the correspondence of the virtual antennacombinations and the physical antenna combinations as Equation 3.

$\begin{matrix}{\begin{bmatrix}z_{0} \\z_{1} \\z_{2} \\z_{3}\end{bmatrix} = {{\frac{1}{2}\begin{bmatrix}a & 0 & b & 0 \\0 & e & 0 & f \\c & 0 & d & 0 \\0 & g & 0 & h\end{bmatrix}} \cdot \begin{bmatrix}y_{0} \\y_{1} \\y_{2} \\y_{3}\end{bmatrix}}} & \left\lbrack {{Eqn}.\mspace{14mu} 3} \right\rbrack\end{matrix}$

In Equation 3, z_(i) (i=0, 1, 2, 3) denotes the signal of the physicalantenna, y_(i) (i=0, 1, 2, 3) denotes the signal of the virtual antenna,i denotes the index of the physical antenna and the virtual antenna, anda, b, c, d, e, f, g, h denote the elements of the corresponding matrix.

When the designed corresponding matrix of Equation 3 is used, thecorresponding matrix should include elements which satisfy a conditionof Equation 4, so as to uniformly distribute the power of the physicalantennas and not to reduce the channel capacity.

$\begin{matrix}{{{a} = {{b} = {{c} = {{d} = {{e} = {{f} = {{g} = {{h} = 1}}}}}}}}{{d = {{- \frac{a^{*}}{b^{*}}}c}},{h = {{- \frac{e^{*}}{f^{*}}}g}}}} & \left\lbrack {{Eqn}.\mspace{14mu} 4} \right\rbrack\end{matrix}$

a, b, c, d, e, f, g, h denote the elements of the corresponding matrix.

In the corresponding matrix of Equation 4, the absolute value of theelements, which are not zero, of the corresponding matrix should be thesame and the unitary property should be satisfied.

To meet the condition (2), the corresponding matrix should be designedby considering characteristics of the precoding codebook. For example,when the transmitting stage designs the corresponding matrix byconsidering the rank 1 precoding vector of the downlink closed-loopcodebook of the LTE standard, the rank 1 precoding vector can berepresented as shown in Table 1.

TABLE 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Precoding vector 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 -j -1 j$\frac{1}{\sqrt{2}}\left( {1 - j} \right)$$\frac{1}{\sqrt{2}}\left( {{- 1} - j} \right)$$\frac{1}{\sqrt{2}}\left( {{- 1} + j} \right)$$\frac{1}{\sqrt{2}}\left( {1 + j} \right)$ 1 -j -1 j 1 1 -1 -1 1 -1 1-1 -j j -j j -1 1 -1 1 1 -1 1 -1 1 j -1 -j$\frac{1}{\sqrt{2}}\left( {{- 1} - j} \right)$$\frac{1}{\sqrt{2}}\left( {1 - j} \right)$$\frac{1}{\sqrt{2}}\left( {1 + j} \right)$$\frac{1}{\sqrt{2}}\left( {{- 1} + j} \right)$ -1 -j 1 j -1 1 1 -1

In Table 1, twelve precoding vectors excluding the fourth throughseventh precoding vectors have the following properties.

(1) All of a 0-th weight and a second weight of the precoding vector arereal numbers. That is, a phase difference between the 0-th weight andthe second weight in each precoding vector is 0° or 180°.

(2) All of a first weight and a third weight of the precoding vector arereal or imaginary numbers. That is, the phase difference between thefirst weight and the third weight in each precoding vector is 0° or180°.

When the corresponding matrix is designed by considering the propertiesof the precoding vector, each element of the corresponding matrix ofEquation 3 should be designed to satisfy Equation 5.

i) a=jb, c=−jd or a=−jb, c=jd

ii) e=jf, g=−jh or e=−jf, g=jh  [Eqn. 5]

The multi-antenna system can design the corresponding matrix of Equation3 to meet the condition of Equation 4 and the condition of Equation 5.In this situation, the corresponding matrix can uniformly distribute thepower of the physical antennas even when the precoding vectors otherthan the fourth through seventh precoding vectors of Table 1 are usedtogether. For example, the corresponding matrix designed based onEquation 3 to meet the condition of Equation 4 and the condition ofEquation 5 is derived as Equation 6.

$\begin{matrix}{{{\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {ja} & 0 \\0 & e & 0 & {je} \\c & 0 & {- {jc}} & 0 \\0 & g & 0 & {- {jg}}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {- {ja}} & 0 \\0 & e & 0 & {je} \\c & 0 & {jc} & 0 \\0 & g & 0 & {- {jg}}\end{bmatrix}}}{{or}\mspace{14mu} {\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {ja} & 0 \\0 & e & 0 & {- {je}} \\c & 0 & {- {jc}} & 0 \\0 & g & 0 & {jg}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {- {ja}} & 0 \\0 & e & 0 & {- {je}} \\c & 0 & {jc} & 0 \\0 & g & 0 & {jg}\end{bmatrix}}}{{where},{{a} = {{c} = {{e} = {{g} = 1}}}}}} & \left\lbrack {{Eqn}.\mspace{14mu} 6} \right\rbrack\end{matrix}$

When a, c, e, g satisfying the condition (3) are applied in thecorresponding matrix of Equation 6, the corresponding matrix can bearranged as expressed in Equation 7.

$\begin{matrix}{{{\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & j & 0 & {- 1} \\{- j} & 0 & {- 1} & 0 \\0 & 1 & 0 & {- j}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- j} & 0 & 1 \\{- j} & 0 & {- 1} & 0 \\0 & {- 1} & 0 & j\end{bmatrix}}}{{or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & j & 0 & {- 1} \\j & 0 & 1 & 0 \\0 & {- 1} & 0 & j\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- j} & 0 & 1 \\j & 0 & 1 & 0 \\0 & 1 & 0 & {- j}\end{bmatrix}}}{{or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- 1} & 0 & {- j} \\j & 0 & {- 1} & 0 \\0 & j & 0 & 1\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & 1 & 0 & j \\j & 0 & {- 1} & 0 \\0 & {- j} & 0 & {- 1}\end{bmatrix}}}{{or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & 1 & 0 & j \\{- j} & 0 & 1 & 0 \\0 & j & 0 & 1\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- 1} & 0 & {- j} \\{- j} & 0 & 1 & 0 \\0 & {- j} & 0 & {- 1}\end{bmatrix}}}{{or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & 1 & 0 & {- j} \\{- j} & 0 & {- 1} & 0 \\0 & j & 0 & {- 1}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- 1} & 0 & j \\{- j} & 0 & {- 1} & 0 \\0 & {- j} & 0 & 1\end{bmatrix}}}{{or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- 1} & 0 & j \\j & 0 & 1 & 0 \\0 & j & 0 & {- 1}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & 1 & 0 & {- j} \\j & 0 & 1 & 0 \\0 & {- j} & 0 & 1\end{bmatrix}}}{{or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & j & 0 & 1 \\j & 0 & {- 1} & 0 \\0 & {- 1} & 0 & {- j}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- j} & 0 & {- 1} \\j & 0 & {- 1} & 0 \\0 & 1 & 0 & j\end{bmatrix}}}{{or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & j & 0 & 1 \\{- j} & 0 & 1 & 0 \\0 & 1 & 0 & j\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- j} & 0 & {- 1} \\{- j} & 0 & 1 & 0 \\0 & {- 1} & 0 & {- j}\end{bmatrix}}}{{{where}\mspace{14mu} {a}} = 1}} & \left\lbrack {{Eqn}.\mspace{14mu} 7} \right\rbrack\end{matrix}$

The condition (3) is that the precoding codebook with the correspondingmatrix applied includes the precoding vector and the equivalent vector.That is, the precoding vector applying any one of the correspondingmatrices of Equation 7 to the 0-th through third precoding vectors andthe eighth through fifteenth precoding vectors of Table 1, is equivalentto any one of the precoding vectors of Table 1.

In the actual implementation, the corresponding matrix of Equation 7increases complexity in the multiplication by

$\frac{a}{\sqrt{2}}.$

Accordingly, when a is set to the value of the phase 45°, 135°, 225°,and 315° such as

$\frac{\left( {1 + j} \right)}{\sqrt{2}},\frac{\left( {1 - j} \right)}{\sqrt{2}},\frac{\left( {{- 1} - j} \right)}{\sqrt{2}},{{and}\mspace{14mu} \frac{\left( {{- 1} + j} \right)}{\sqrt{2}}},$

the transmitting stage can lower the complexity by reducing themultiplication. For example, when a is set to

$\frac{\left( {1 + j} \right)}{\sqrt{2}},$

the corresponding matrix can be expressed as

$\begin{matrix}{{Equation}\mspace{14mu} 8.} & \; \\{\frac{1}{2}\begin{bmatrix}{1 + j} & 0 & {{- 1} + j} & 0 \\0 & {{- 1} + j} & 0 & {{- 1} - j} \\{1 - j} & 0 & {{- 1} - j} & 0 \\0 & {1 + j} & 0 & {1 - j}\end{bmatrix}} & \left\lbrack {{Eqn}.\mspace{14mu} 8} \right\rbrack\end{matrix}$

When a is set to

$\frac{\left( {1 + j} \right)}{\sqrt{2}}$

in Equation 8, the complexity can be reduced by mapping the physicalantennas merely with addition of the real component and the imaginarycomponent of the virtual antenna signal.

In this embodiment, the multi-antenna system designs the correspondingmatrix by considering the rank 1 precoding vector of the downlinkclosed-loop codebook of the LIE standard.

Alternatively, when the precoding vectors of rank 2, 3 and 4 of thedownlink closed-loop codebook are considered, the multi-antenna systemcan design the corresponding matrix in the above-stated manner.

Now, a method of the transmitting stage for sending the signal using thevirtual antenna mapping is explained.

FIG. 2 illustrates a method for sending a signal at the transmittingstage in the multi-antenna system according to an embodiment of thepresent invention.

In step 201, the transmitting stage generates the virtual antennasignals. That is, the transmitting stage generates the reference signalfor each virtual antenna and the signal for the traffic channel.

In step 203, the transmitting stage determines the precoding weightdetermined based on the virtual antenna mapping. For example, when theclosed-loop scheme is used, a base station determines the precodingweight by considering the codebook index provided from a mobile station.In so doing, when the corresponding matrix is used together, the basestation instructs the mobile station not to use the precoding code whichcannot uniformly distribute the power of the physical antennas. Hence,even when the corresponding matrix is used together, the base stationcan use only the precoding code which can uniformly distribute the powerof the physical antennas.

In step 205, the transmitting stage precodes each virtual antenna signalwith the confirmed precoding weight.

In step 207, the transmitting stage determines the corresponding matrixdetermined based on the precoding weight. For example, the transmittingstage confirms the corresponding matrix as expressed in Equation 3,which satisfies the conditions of Equation 4 and Equation 5.

In step 209, the transmitting stage maps the virtual antenna signals tothe physical antennas using the corresponding matrix. That is, thetransmitting stage generates the physical antenna signals by linearlycombining the virtual antenna signals using the corresponding matrix.

Next, the transmitting stage finishes this process. The transmittingstage sends the generated physical antenna signals over the respectivephysical antennas.

Although it is not illustrated here, the transmitting stage precodes thevirtual antenna signals, and generates the virtual antenna signals tosend over the respective virtual antennas by combining the precodedsignal with the reference signal to send over the virtual antennas.

In this embodiment, the transmitting stage precodes the virtual antennasignal.

Alternatively, the transmitting stage may generate the virtual antennasignals to send over the respective virtual antennas by precoding atleast one traffic channel. The transmitting stage generates the virtualantenna signals to send over the respective virtual antennas bycombining the virtual antenna signals generated using the precoding andthe reference signal to send over the virtual antennas.

Hereafter, a structure of the transmitting stage for mapping the virtualantennas and the physical antennas is described.

FIG. 3 is a block diagram of the transmitting stage in the multi-antennasystem according to an embodiment of the present invention.

The transmitting stage of FIG. 3 includes a traffic channel signalgenerator 300, encoders 302-1 through 302-N_(s), modulators 304-1through 304-N_(s), a precoder 306, a virtual antenna signal generator308, a virtual antenna mapper 310, Radio Frequency (RF) processors 312-1through 312-N_(T), a reference signal generator 314, a mappingcontroller 316, a weight controller 318, and a feedback receiver 320.

The traffic channel signal generator 300 generates N_(s) trafficchannels having independent information. N_(s) denotes the number ofstreams spatially separated, and ranges from 1 to N_(k). Herein, N_(k)denotes the number of the virtual antennas.

The encoders 302-1 through 302-N_(s) encode the traffic channels outputfrom the traffic channel signal generator 300 at a modulation leveladequate for the channel state. Herein, the modulation level indicates aModulation and Coding Scheme (MCS) level.

The modulators 304-1 through 304-N_(s) modulate the encoded signalsoutput from the encoders 302-1 through 302-N_(s) according to themodulation level suitable for the channel state.

The precoder 306 precodes the N_(s) traffic channels output from themodulators 304-1 through 304-N_(s) to N_(k) virtual antenna signals witha precode provided from the weight controller 318.

The weight controller 318 generates the precode by taking account of thecodebook index output from the feedback receiver 320.

The weight controller 318 instructs the serviced receiving stage not touse the precoding vector which cannot be used with the correspondingmatrix. For example, when the codebook of the rank 1 precoding vector ofthe downlink closed-loop codebook of the LIE standard is used, theweight controller 318 instructs the receiving stage not to use thefourth through seventh precoding vectors.

The feedback receiver 320 receives feedback information of the receivingstage.

The virtual antenna signal generator 308 generates the virtual antennasignals to send over the respective virtual antennas by combining theprecoded traffic channel signals output from the precoder 306 and thereference signal output from the reference signal generator 314.

The reference signal generator 314 generates the virtual antennareference signal to send over the virtual antennas. For example, thereference signal includes a pilot.

The virtual antenna mapper 310 maps the virtual antenna signals fed fromthe virtual antenna signal generator 308 to the physical antennas usingthe corresponding matrix provided from the mapping controller 316. Morespecifically, the virtual antenna mapper 310 generates the signals forthe physical antennas by linearly combining the virtual antenna signalsoutput from the virtual antenna signal generator 308 using thecorresponding matrix provided from the mapping controller 316.

The mapping controller 316 determines the corresponding matrix to mapthe virtual antennas and the physical antennas at the virtual antennamapper 310. For example, the mapping controller 316 selects any one ofthe corresponding matrices of Equation 7 designed based on Equation 3which meets the conditions of Equation 4 and Equation 5. Thecorresponding matrices of Equation 7 are designed by taking into accountthe properties of the precoding codebook and to satisfy the conditions(1), (2) and (3). For example, the mapping controller 316 may generatethe corresponding matrix of Equation 3 which meets the conditions ofEquation 4 and Equation 5. In this situation, the mapping controller 316generates the corresponding matrix by taking into account the propertiesof the precoding codebook and to satisfy the conditions (1), (2) and(3).

The RF processors 312-1 through 312-N_(T) convert the physical antennasignals output from the virtual antenna mapper 310 to analog signals.Next, the RF processors 312-1 through 312-N_(T) convert the analogsignals to RF signals and transmit the RF signals over the correspondingphysical antenna.

As set forth above, by mapping the virtual antennas and the physicalantennas in the many-to-many correspondence in the multi-antenna system,it is advantageous to uniformly distribute the power to the physicalantennas.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

1. A method for transmitting a signal at a transmitting stage of awireless communication system, the method comprising: generating atleast two virtual antenna signals for at least two virtual antennas;generating at least two physical antenna signals by applying acorresponding matrix to the at least two virtual antenna signals, thecorresponding matrix mapping the at least two virtual antennas and theat least two physical antennas in a many-to-many relation; andtransmitting the at least two physical antenna signals over respectivephysical antennas.
 2. The method of claim 1, further comprising: aftergenerating the at least two virtual antenna signals, precoding the atleast two virtual antenna signals, wherein the generating of thephysical antenna signals comprises: generating at least two physicalantenna signals by applying the corresponding matrix to the at least twoprecoded virtual antenna signals.
 3. The method of claim 1, wherein thegenerating of the physical antenna signals comprises: generating atleast two physical antenna signals by linearly combining the at leasttwo virtual antenna signals using the corresponding matrix.
 4. Themethod of claim 1, wherein the generating of the physical antennasignals comprises: when there are four virtual antennas and fourphysical antennas, generating two physical antenna signals by linearlycombining the 0-th virtual antenna signal and the second virtual antennasignal, and generating two different physical antenna signals bylinearly combining the first virtual antenna signal and the thirdvirtual antenna signal.
 5. The method of claim 1, wherein, when thereare four virtual antennas and four physical antennas, the correspondingmatrix is expressed as the following equation:$\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & b & 0 \\0 & e & 0 & f \\c & 0 & d & 0 \\0 & g & 0 & h\end{bmatrix}$ where a, b, c, d, e, f, g, h denote elements of thecorresponding matrix defined to have unitary properties of thecorresponding matrix, and the elements indicate complex numbers of thesame absolute value.
 6. The method of claim 1, wherein, when there arefour virtual antennas and four physical antennas, the correspondingmatrix is any one of corresponding matrices of the following equation:${\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {ja} & 0 \\0 & e & 0 & {je} \\c & 0 & {- {jc}} & 0 \\0 & g & 0 & {- {jg}}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {- {ja}} & 0 \\0 & e & 0 & {je} \\c & 0 & {jc} & 0 \\0 & g & 0 & {- {jg}}\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {ja} & 0 \\0 & e & 0 & {- {je}} \\c & 0 & {- {jc}} & 0 \\0 & g & 0 & {jg}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {- {ja}} & 0 \\0 & e & 0 & {- {je}} \\c & 0 & {jc} & 0 \\0 & g & 0 & {jg}\end{bmatrix}}$ where, a = c = e = g = 1 where a, c, e, g denoteelements of the corresponding matrix defined to have unitary propertiesof the corresponding matrix, and the elements indicate random complexnumbers of the absolute number
 1. 7. The method of claim 1, wherein,when there are four virtual antennas and four physical antennas, thecorresponding matrix is any one of corresponding matrices of thefollowing equation: ${\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & j & 0 & {- 1} \\{- j} & 0 & {- 1} & 0 \\0 & 1 & 0 & {- j}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- j} & 0 & 1 \\{- j} & 0 & {- 1} & 0 \\0 & {- 1} & 0 & j\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & j & 0 & {- 1} \\j & 0 & 1 & 0 \\0 & {- 1} & 0 & j\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- j} & 0 & 1 \\j & 0 & 1 & 0 \\0 & 1 & 0 & {- j}\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- 1} & 0 & {- j} \\j & 0 & {- 1} & 0 \\0 & j & 0 & 1\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & 1 & 0 & j \\j & 0 & {- 1} & 0 \\0 & {- j} & 0 & {- 1}\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & 1 & 0 & j \\{- j} & 0 & 1 & 0 \\0 & j & 0 & 1\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- 1} & 0 & {- j} \\{- j} & 0 & 1 & 0 \\0 & {- j} & 0 & {- 1}\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & 1 & 0 & {- j} \\{- j} & 0 & {- 1} & 0 \\0 & j & 0 & {- 1}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- 1} & 0 & j \\{- j} & 0 & {- 1} & 0 \\0 & {- j} & 0 & 1\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- 1} & 0 & j \\j & 0 & 1 & 0 \\0 & j & 0 & {- 1}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & 1 & 0 & {- j} \\j & 0 & 1 & 0 \\0 & {- j} & 0 & 1\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & j & 0 & 1 \\j & 0 & {- 1} & 0 \\0 & {- 1} & 0 & {- j}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- j} & 0 & {- 1} \\j & 0 & {- 1} & 0 \\0 & 1 & 0 & j\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & j & 0 & 1 \\{- j} & 0 & 1 & 0 \\0 & 1 & 0 & j\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- j} & 0 & {- 1} \\{- j} & 0 & 1 & 0 \\0 & {- 1} & 0 & {- j}\end{bmatrix}}$ where  a =
 1. 8. The method of claim 1, furthercomprising: when a closed-loop precoding scheme is used, instructing areceiving stage not to use at least one precoding vector that isunusable with the corresponding matrix in a codebook.
 9. The method ofclaim 8, wherein the at least one precoding vector comprises a precodingvector that does not satisfy all of a condition that both of a 0-thweight and a second weight of the precoding vector are real numbers, anda condition that both of a first weight and a third weight of theprecoding vector are real or imaginary numbers.
 10. An apparatus fortransmitting a signal at a transmitting stage of a wirelesscommunication system, the apparatus comprising: at least two physicalantennas; a signal generator configured to generate at least two virtualantenna signals for at least two virtual antennas; and a virtual antennamapper configured to: generate at least two physical antenna signals byapplying a corresponding matrix to the at least two virtual antennasignals, the corresponding matrix mapping the at least two virtualantennas and the at least two physical antennas in a many-to-manyrelation; and provide the at least two physical antenna signals to therespective physical antennas.
 11. The apparatus of claim 10, furthercomprising: a precoder configured to precode the at least two virtualantenna signals generated by the signal generator and provide theprecoded signals to the virtual antenna mapper.
 12. The apparatus ofclaim 10, wherein the virtual antenna mapper generates at least twophysical antenna signals by linearly combining the at least two virtualantenna signals using the corresponding matrix.
 13. The apparatus ofclaim 10, wherein, when there are four virtual antennas and fourphysical antennas, the virtual antenna mapper generates two physicalantenna signals by linearly combining the 0-th virtual antenna signaland the second virtual antenna signal, and generates two differentphysical antenna signals by linearly combining the first virtual antennasignal and the third virtual antenna signal.
 14. The apparatus of claim10, wherein, when there are four virtual antennas and four physicalantennas, the corresponding matrix is expressed as the followingequation: $\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & b & 0 \\0 & e & 0 & f \\c & 0 & d & 0 \\0 & g & 0 & h\end{bmatrix}$ where a, b, c, d, e, f, g, h denote elements of thecorresponding matrix defined to have unitary properties of thecorresponding matrix, and the elements indicate complex numbers of thesame absolute value.
 15. The apparatus of claim 10, wherein, when thereare four virtual antennas and four physical antennas, the correspondingmatrix is any one of corresponding matrices of the following equation:${\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {ja} & 0 \\0 & e & 0 & {je} \\c & 0 & {- {jc}} & 0 \\0 & g & 0 & {- {jg}}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {- {ja}} & 0 \\0 & e & 0 & {je} \\c & 0 & {jc} & 0 \\0 & g & 0 & {- {jg}}\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {ja} & 0 \\0 & e & 0 & {- {je}} \\c & 0 & {- {jc}} & 0 \\0 & g & 0 & {jg}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{1}{\sqrt{2}}\begin{bmatrix}a & 0 & {- {ja}} & 0 \\0 & e & 0 & {- {je}} \\c & 0 & {jc} & 0 \\0 & g & 0 & {jg}\end{bmatrix}}$ where, a = c = e = g = 1 where a, c, e, g denoteelements of the corresponding matrix defined to have unitary propertiesof the corresponding matrix, and the elements indicate random complexnumbers of the absolute number
 1. 16. The apparatus of claim 10,wherein, when there are four virtual antennas and four physicalantennas, the corresponding matrix is any one of corresponding matricesof the following equation: ${\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & j & 0 & {- 1} \\{- j} & 0 & {- 1} & 0 \\0 & 1 & 0 & {- j}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- j} & 0 & 1 \\{- j} & 0 & {- 1} & 0 \\0 & {- 1} & 0 & j\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & j & 0 & {- 1} \\j & 0 & 1 & 0 \\0 & {- 1} & 0 & j\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- j} & 0 & 1 \\j & 0 & 1 & 0 \\0 & 1 & 0 & {- j}\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- 1} & 0 & {- j} \\j & 0 & {- 1} & 0 \\0 & j & 0 & 1\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & 1 & 0 & j \\j & 0 & {- 1} & 0 \\0 & {- j} & 0 & {- 1}\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & 1 & 0 & j \\{- j} & 0 & 1 & 0 \\0 & j & 0 & 1\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- 1} & 0 & {- j} \\{- j} & 0 & 1 & 0 \\0 & {- j} & 0 & {- 1}\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & 1 & 0 & {- j} \\{- j} & 0 & {- 1} & 0 \\0 & j & 0 & {- 1}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- 1} & 0 & j \\{- j} & 0 & {- 1} & 0 \\0 & {- j} & 0 & 1\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & {- 1} & 0 & j \\j & 0 & 1 & 0 \\0 & j & 0 & {- 1}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & j & 0 \\0 & 1 & 0 & {- j} \\j & 0 & 1 & 0 \\0 & {- j} & 0 & 1\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & j & 0 & 1 \\j & 0 & {- 1} & 0 \\0 & {- 1} & 0 & {- j}\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- j} & 0 & {- 1} \\j & 0 & {- 1} & 0 \\0 & 1 & 0 & j\end{bmatrix}}$ ${or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & j & 0 & 1 \\{- j} & 0 & 1 & 0 \\0 & 1 & 0 & j\end{bmatrix}}\mspace{14mu} {or}\mspace{14mu} {\frac{a}{\sqrt{2}}\begin{bmatrix}1 & 0 & {- j} & 0 \\0 & {- j} & 0 & {- 1} \\{- j} & 0 & 1 & 0 \\0 & {- 1} & 0 & {- j}\end{bmatrix}}$ where  a =
 1. 17. The apparatus of claim 10, furthercomprising: a weight controller configured, when a closed-loop precodingscheme is used, to instruct a receiving stage not to use at least oneprecoding vector that is unusable with the corresponding matrix in acodebook.
 18. The apparatus of claim 17, wherein the weight controllerrecognizes a precoding vector that does not satisfy all of a conditionthat both of a 0-th weight and a second weight of the precoding vectorare real numbers, and a condition that both of a first weight and athird weight of the precoding vector are real or imaginary numbers, asthe precoding vector unusable with the corresponding matrix.
 19. Theapparatus of claim 10, further comprising: at least two encoders, eachencoder configured to encode one of the at least two virtual antennasignals.
 20. The apparatus of claim 10, further comprising: a referencesignal generator configured to generate a virtual antenna referencesignal that is sent over the at least two virtual antennas.